Improve performance of enumerate() with optimization disabled

Reviewed By: yfeldblum, WillerZ

Differential Revision: D6682606

fbshipit-source-id: 5a203a849e96d3020cf9ad2669451122954c2199

folly/container/Enumerate.h

 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2017-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -19,6 +19,7 @@
 #include <iterator>
 #include <memory>
 
+#include <folly/CPortability.h>
 #include <folly/portability/SysTypes.h>
 
 /**
@@ -64,11 +65,13 @@ struct MakeConst<T*> {
 // second overload will be SFINAEd out in that case. Otherwise, the
 // second is preferred in the partial order for getPointer(_, 0).
 template <class Iterator>
-auto getPointer(const Iterator& it, long) -> decltype(std::addressof(*it)) {
+FOLLY_ALWAYS_INLINE auto getPointer(const Iterator& it, long)
+    -> decltype(std::addressof(*it)) {
   return std::addressof(*it);
 }
 template <class Iterator>
-auto getPointer(const Iterator& it, int) -> decltype(it.operator->()) {
+FOLLY_ALWAYS_INLINE auto getPointer(const Iterator& it, int)
+    -> decltype(it.operator->()) {
   return it.operator->();
 }
 
@@ -85,21 +88,22 @@ class Enumerator {
     using pointer = typename std::iterator_traits<Iterator>::pointer;
     using iterator_category = std::input_iterator_tag;
 
-    explicit Proxy(const Enumerator* e) : it_(e->it_), index(e->idx_) {}
+    FOLLY_ALWAYS_INLINE explicit Proxy(const Enumerator& e)
+        : it_(e.it_), index(e.idx_) {}
 
     // Non-const Proxy: Forward constness from Iterator.
-    reference operator*() {
+    FOLLY_ALWAYS_INLINE reference operator*() {
       return *it_;
     }
-    pointer operator->() {
+    FOLLY_ALWAYS_INLINE pointer operator->() {
       return getPointer(it_, 0);
     }
 
     // Const Proxy: Force const references.
-    typename MakeConst<reference>::type operator*() const {
+    FOLLY_ALWAYS_INLINE typename MakeConst<reference>::type operator*() const {
       return *it_;
     }
-    typename MakeConst<pointer>::type operator->() const {
+    FOLLY_ALWAYS_INLINE typename MakeConst<pointer>::type operator->() const {
       return getPointer(it_, 0);
     }
 
@@ -110,24 +114,24 @@ class Enumerator {
     const size_t index;
   };
 
-  Proxy operator*() const {
-    return Proxy(this);
+  FOLLY_ALWAYS_INLINE Proxy operator*() const {
+    return Proxy(*this);
   }
 
-  Enumerator& operator++() {
+  FOLLY_ALWAYS_INLINE Enumerator& operator++() {
     ++it_;
     ++idx_;
     return *this;
   }
 
   template <typename OtherIterator>
-  bool operator==(const Enumerator<OtherIterator>& rhs) {
+  FOLLY_ALWAYS_INLINE bool operator==(const Enumerator<OtherIterator>& rhs) {
     return it_ == rhs.it_;
   }
 
   template <typename OtherIterator>
-  bool operator!=(const Enumerator<OtherIterator>& rhs) {
-    return !(*this == rhs);
+  FOLLY_ALWAYS_INLINE bool operator!=(const Enumerator<OtherIterator>& rhs) {
+    return !(it_ == rhs.it_);
   }
 
  private:

folly/container/Foreach.h

 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2017-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -121,9 +121,9 @@ FOLLY_CPP14_CONSTEXPR decltype(auto) fetch(Sequence&& sequence, Index&& index);
 } // namespace folly
 
 /**
- * Everything below this is deprecated.  Use the folly::for_each algorithm above
- * instead
+ * Everything below is deprecated.
  */
+
 /*
  * Form a local variable name from "FOR_EACH_" x __LINE__, so that
  * FOR_EACH can be nested without creating shadowed declarations.
@@ -159,9 +159,9 @@ FOLLY_CPP14_CONSTEXPR decltype(auto) fetch(Sequence&& sequence, Index&& index);
            i != _FE_ANON(s2_).rend(); ++i)
 
 /*
- * If you just want the element values, please use this (ranges-v3) construct:
+ * If you just want the element values, please use this construct:
  *
- *    for (auto&& element : collection | view::zip(view::ints))
+ *    for (auto&& element : folly::enumerate(collection))
  *
  * If you need access to the iterators please write an explicit iterator loop
  * and use a counter variable

folly/container/test/ForeachBenchmark.cpp

 /*
- * Copyright 2017 Facebook, Inc.
+ * Copyright 2017-present Facebook, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -14,12 +14,14 @@
  * limitations under the License.
  */
 
-#include <folly/container/Foreach.h>
+#include <algorithm>
+#include <map>
 
 #include <folly/Benchmark.h>
-#include <folly/portability/GTest.h>
-
-#include <map>
+#include <folly/Random.h>
+#include <folly/container/Enumerate.h>
+#include <folly/container/Foreach.h>
+#include <folly/init/Init.h>
 
 using namespace folly;
 using namespace folly::detail;
@@ -31,10 +33,14 @@ using namespace folly::detail;
 //    iter->second as is, without assigning to local variables.
 // 3. Use FOR_EACH_KV loop to iterate through the map.
 
-std::map<int, std::string> bmMap; // For use in benchmarks below.
+// For use in benchmarks below.
+std::map<int, std::string> bmMap;
 std::vector<int> vec_one;
 std::vector<int> vec_two;
 
+// Smallest type to isolate iteration overhead.
+std::vector<char> vec_char;
+
 void setupBenchmark(size_t iters) {
   bmMap.clear();
   for (size_t i = 0; i < iters; ++i) {
@@ -47,6 +53,12 @@ void setupBenchmark(size_t iters) {
   vec_two.resize(iters);
 }
 
+void setupCharVecBenchmark(size_t iters) {
+  vec_char.resize(iters);
+  std::generate(
+      vec_char.begin(), vec_char.end(), [] { return Random::rand32(128); });
+}
+
 BENCHMARK(ForEachFunctionNoAssign, iters) {
   BenchmarkSuspender suspender;
 
@@ -330,13 +342,61 @@ BENCHMARK(ForEachRangeR, iters) {
   doNotOptimizeAway(sum);
 }
 
-int main(int argc, char** argv) {
-  testing::InitGoogleTest(&argc, argv);
-  gflags::ParseCommandLineFlags(&argc, &argv, true);
-  auto r = RUN_ALL_TESTS();
-  if (r) {
-    return r;
+BENCHMARK(CharVecForRange, iters) {
+  BENCHMARK_SUSPEND {
+    setupCharVecBenchmark(iters);
+  }
+  size_t sum = 0;
+  for (auto& c : vec_char) {
+    sum += c;
+  }
+  doNotOptimizeAway(sum);
+}
+
+BENCHMARK(CharVecForRangeExplicitIndex, iters) {
+  BENCHMARK_SUSPEND {
+    setupCharVecBenchmark(iters);
+  }
+  size_t sum = 0;
+  size_t index = 0;
+  for (auto& c : vec_char) {
+    sum += c * index;
+    ++index;
+  }
+  doNotOptimizeAway(sum);
+}
+
+BENCHMARK(CharVecForEach, iters) {
+  BENCHMARK_SUSPEND {
+    setupCharVecBenchmark(iters);
+  }
+  size_t sum = 0;
+  folly::for_each(vec_char, [&](auto& c) { sum += c; });
+  doNotOptimizeAway(sum);
+}
+
+BENCHMARK(CharVecForEachIndex, iters) {
+  BENCHMARK_SUSPEND {
+    setupCharVecBenchmark(iters);
+  }
+  size_t sum = 0;
+  folly::for_each(vec_char, [&](auto& c, auto index) { sum += c * index; });
+  doNotOptimizeAway(sum);
+}
+
+BENCHMARK(CharVecForRangeEnumerate, iters) {
+  BENCHMARK_SUSPEND {
+    setupCharVecBenchmark(iters);
+  }
+  size_t sum = 0;
+  for (auto it : enumerate(vec_char)) {
+    sum += *it * it.index;
   }
+  doNotOptimizeAway(sum);
+}
+
+int main(int argc, char** argv) {
+  folly::init(&argc, &argv);
   runBenchmarks();
   return 0;
 }